Regulatory T cell Immunobiology Specialization and Stability in mucosal immunoregulation and tissue homestasis

Background: In order to maintain immune homeostasis, the immune system must translate a wide variety of environmental insults such as pollutants, commensal bacteria, and pathogens via the mucosal surfaces and regulate subsequent immune responses. The mammalian immune system has evolved elaborate ways to limit aberrant immune responses and emerging data demonstrate that Foxp3-expressing regulatory T (TREG) cells play a critical role in the process at mucosal surfaces. Interestingly, TREG cells in secondary lymphoid organs and tissues are different indicating modulation by the local tissue microenvironment. However the interactions and mediators influencing this tissue specific modulation of TREG function are unknown and hence it is important to further our understanding of the critical determinants of TREG cell specialization and stability. Specialized TREG cells that potently suppress tissue damage have been described in mice and this represents a novel aspect of TREG cell immunobiology. However, it is unclear whether human TREG cells are also specialized to regulate different types of inflammation at different sites and in response to different antigens. In addition, we have identified that murine TREG cells are often unstable and can convert into effector T cells at mucosal surfaces (unpublished observations). Therefore it is clear that basic biological investigation of TREG function especially in tissues is required to further our understanding of the immunoregulatory behaviour of TREGs in these tissues and the mechanisms by which they maintain immune homeostasis.We hypothesize that murine and human TREG cells are indeed plastic and can convert into effector T cells, contributing to inflammation. To investigate this hypothesis we will use 1) in-vitro and in-vivo models to probe the role of the TREG in inflammatory events and tissue homeostasis; 2) human T cell lines and 3) primary cells from healthy donors to explore the basic biological phenomenon of human and murine TREG specialization and TREG stability. Project Questions, Aims and Hypotheses:
1. Do murine and human TREG cells become specialized in the mucosal tissue? We, and others, have identified that TREG cells co-opt specific features including the appropriate transcriptional machinery to suppress particular TH cells, including TH1, TH2 and TH17 cells. We aim to identify whether human (PBMC- or mucosal tissue-derived) or murine (lymph node or mucosal tissue-derived) TREG cells adopt a 'specialized' phenotype to control different types of immune response. We hypothesize that both human and murine TREG cells will become specialized to control specific TH responses at mucosal surfaces. 2. Are murine and human TREG cells plastic? We recently identified that murine TREG cells are unstable and can convert to TH2 cells in the gut contributing to immunity. We hypothesize that murine and human TREG cells are unstable and can convert to effector T cells. To test whether TREG cells become specialized at mucosal surfaces (Aim 1) and whether TREG cells are plastic at mucosal surfaces (Aim 2) we have generated a suite of reporter mice that allow tracking of TREG movement and function during an ongoing immune response. Utilising these transgenic mice we will determine whether TREG cells become specialized to control distinct responses and whether TREG cells convert to Th1, Th2 or Th17 cells. 3. Is TREG function influenced by contact with structural cells and tissue specific mediators? We hypothesize that tissue specific signals either via cell-cell contact and/or soluble mediators driven by the type of inflammation in the mucosal tissue will influence TREG function. Here we aim to model this using human primary epithelial cells co-cultured with TREGs (and possibly dendritic cells) to mimic aspects of this interaction. This human in vitro system will allow investigation of the impact of co-culture on TREG biology and the influence of pro-inflammatory stimuli on the epithelium a